Nuclear delivery of recombinant OCT4 by chitosan nanoparticles for transgene-free generation of protein-induced pluripotent stem cells.

Protein-based reprogramming of somatic cells is a non-genetic approach for the generation of induced pluripotent stem cells (iPSCs), whereby reprogramming factors, such as OCT4, SOX2, KLF4 and c-MYC, are delivered as functional proteins. The technique is considered safer than transgenic methods, but, unfortunately, most protein-based protocols provide very low reprogramming efficiencies. In this study, we developed exemplarily a nanoparticle (NP)-based delivery system for the reprogramming factor OCT4. To this end, we expressed human OCT4 in Sf9 insect cells using a baculoviral expression system. Recombinant OCT4 showed nuclear localization in Sf9 cells indicating proper protein folding. In comparison to soluble OCT4 protein, encapsulation of OCT4 in nuclear-targeted chitosan NPs strongly stabilized its DNA-binding activity even under cell culture conditions. OCT4-loaded NPs enabled cell treatment with high micromolar concentrations of OCT4 and successfully delivered active OCT4 into human fibroblasts. Chitosan NPs therefore provide a promising tool for the generation of transgene-free iPSCs.

Novel AKT phosphorylation sites identified in the pluripotency factors OCT4, SOX2 and KLF4.

The four OSKM factors OCT4, SOX2, KLF4 and c-MYC are key transcription factors modulating pluripotency, self-renewal and tumorigenesis in stem cells. However, although their transcriptional targets have been extensively studied, little is known about how these factors are regulated at the posttranslational level. In this study, we established an in vitro system to identify phosphorylation patterns of the OSKM factors by AKT kinase. OCT4, SOX2, KLF4 and c-MYC were expressed in Sf9 insect cells employing the baculoviral expression system. OCT4, SOX2 and KLF4 were localized in the nucleus of insect cells, allowing their easy purification to near homogeneity upon nuclear fractionation. All transcription factors were isolated as biologically active DNA-binding proteins. Using in vitro phosphorylation and mass spectrometry-based phosphoproteome analyses several novel and known AKT phosphorylation sites could be identified in OCT4, SOX2 and KLF4.

Molecular and functional interactions between AKT and SOX2 in breast carcinoma.

The transcription factor SOX2 is a key regulator of pluripotency in embryonic stem cells and plays important roles in early organogenesis. Recently, SOX2 expression was documented in various cancers and suggested as a cancer stem cell (CSC) marker. Here we identify the Ser/Thr-kinase AKT as an upstream regulator of SOX2 protein turnover in breast carcinoma (BC). SOX2 and pAKT are co-expressed and co-regulated in breast CSCs and depletion of either reduces clonogenicity. Ectopic SOX2 expression restores clonogenicity and in vivo tumorigenicity of AKT-inhibited cells, suggesting that SOX2 acts as a functional downstream AKT target. Mechanistically, we show that AKT physically interacts with the SOX2 protein to modulate its subcellular distribution. AKT kinase inhibition results in enhanced cytoplasmic retention of SOX2, presumably via impaired nuclear import, and in successive cytoplasmic proteasomal degradation of the protein. In line, blockade of either nuclear transport or proteasomal degradation rescues SOX2 expression in AKT-inhibited BC cells. Finally, AKT inhibitors efficiently suppress the growth of SOX2-expressing putative cancer stem cells, whereas conventional chemotherapeutics select for this population. Together, our results suggest the AKT/SOX2 molecular axis as a regulator of BC clonogenicity and AKT inhibitors as promising drugs for the treatment of SOX2-positive BC.

High glutathione and glutathione peroxidase-2 levels mediate cell-type-specific DNA damage protection in human induced pluripotent stem cells.

Pluripotent stem cells must strictly maintain genomic integrity to prevent transmission of mutations. In human induced pluripotent stem cells (iPSCs), we found that genome surveillance is achieved via two ways, namely, a hypersensitivity to apoptosis and a very low accumulation of DNA lesions. The low apoptosis threshold was mediated by constitutive p53 expression and a marked upregulation of proapoptotic p53 target genes of the BCL-2 family, ensuring the efficient iPSC removal upon genotoxic insults. Intriguingly, despite the elevated apoptosis sensitivity, both mitochondrial and nuclear DNA lesions induced by genotoxins were less frequent in iPSCs compared to fibroblasts. Gene profiling identified that mRNA expression of several antioxidant proteins was considerably upregulated in iPSCs. Knockdown of glutathione peroxidase-2 and depletion of glutathione impaired protection against DNA lesions. Thus, iPSCs ensure genomic integrity through enhanced apoptosis induction and increased antioxidant defense, contributing to protection against DNA damage.

Sulforaphane protects from T cell-mediated autoimmune disease by inhibition of IL-23 and IL-12 in dendritic cells.

Sulforaphane (SFN), an isothiocyanate, is part of an important group of naturally occurring small molecules with anti-inflammatory properties. The published reports are best conceivable with an inhibition of T cell function, but the mode of action remains unknown. We therefore analyzed the effect of SFN on T cell-mediated autoimmune disease. Feeding mice with SFN protected from severe experimental autoimmune encephalomyelitis. Disease amelioration was associated with reduced IL-17 and IFN-γ expression in draining lymph nodes. In vitro, SFN treatment of T cells did not directly alter T cell cytokine secretion. In contrast, SFN treatment of dendritic cells (DCs) inhibited TLR4-induced IL-12 and IL-23 production, and severely suppressed Th1 and Th17 development of T cells primed by SFN-treated DCs. SFN regulated the activity of the TLR4-induced transcription factor NF-κB, without affecting the degradation of its inhibitor IκB-α. Instead, SFN treatment of DCs resulted in strong expression of the stress response protein heme oxygenase-1 (HO-1), which interacts with and thereby inhibits NF-κB p65. Consistent with these findings, HO-1 bound to p65 and subsequently inhibited the p65 activity at the IL23a and IL12b promoters. Importantly, SFN suppressed Il23a and Il12b expression in vivo and silenced Th17/Th1 responses within the CNS. Thus, our data show that SFN improves Th17/Th1-mediated autoimmune disease by inducing HO-1 and inhibiting NF-κB p65-regulated IL-23 and IL-12 expression.

LORD-Q: a long-run real-time PCR-based DNA-damage quantification method for nuclear and mitochondrial genome analysis.

DNA damage is tightly associated with various biological and pathological processes, such as aging and tumorigenesis. Although detection of DNA damage is attracting increasing attention, only a limited number of methods are available to quantify DNA lesions, and these techniques are tedious or only detect global DNA damage. In this study, we present a high-sensitivity long-run real-time PCR technique for DNA-damage quantification (LORD-Q) in both the mitochondrial and nuclear genome. While most conventional methods are of low-sensitivity or restricted to abundant mitochondrial DNA samples, we established a protocol that enables the accurate sequence-specific quantification of DNA damage in >3-kb probes for any mitochondrial or nuclear DNA sequence. In order to validate the sensitivity of this method, we compared LORD-Q with a previously published qPCR-based method and the standard single-cell gel electrophoresis assay, demonstrating a superior performance of LORD-Q. Exemplarily, we monitored induction of DNA damage and repair processes in human induced pluripotent stem cells and isogenic fibroblasts. Our results suggest that LORD-Q provides a sequence-specific and precise method to quantify DNA damage, thereby allowing the high-throughput assessment of DNA repair, genotoxicity screening and various other processes for a wide range of life science applications.

Nor-1, a novel incretin-responsive regulator of insulin genes and insulin secretion.

B-cell failure at the onset of type 2 diabetes is caused by a decline in ß-cell function in the postprandial state and loss of pancreatic ß-cell mass. Recently, we showed an association between increased insulin secretion and a single nucleotide polymorphism (SNP), SNP rs12686676, in the NR4A3 gene locus encoding the nuclear receptor Nor-1. Nor-1 is expressed in ß-cells, however, not much is known about its function with regard to insulin gene expression and insulin secretion. Nor-1 is induced in a glucose-/incretin-dependent manner via the PKA pathway and directly induces insulin gene expression. Additionally, it stimulates insulin secretion possibly via regulation of potentially important genes in insulin exocytosis. Moreover, we show that the minor allele of NR4A3 SNP rs12686676 fully rescues incretin resistance provoked by a well-described polymorphism in TCF7L2. Thus, Nor-1 represents a promising new target for pharmacological intervention to fight diabetes.

SOX2 expression associates with stem cell state in human ovarian carcinoma.

The SRY-related HMG-box family of transcription factors member SOX2 regulates stemness and pluripotency in embryonic stem cells and plays important roles during early embryogenesis. More recently, SOX2 expression was documented in several tumor types including ovarian carcinoma, suggesting an involvement of SOX2 in regulation of cancer stem cells (CSC). Intriguingly, however, studies exploring the predictive value of SOX2 protein expression with respect to histopathologic and clinical parameters report contradictory results in individual tumors, indicating that SOX2 may play tumor-specific roles. In this report, we analyze the functional relevance of SOX2 expression in human ovarian carcinoma. We report that in human serous ovarian carcinoma (SOC) cells, SOX2 expression increases the expression of CSC markers, the potential to form tumor spheres, and the in vivo tumor-initiating capacity, while leaving cellular proliferation unaltered. Moreover, SOX2-expressing cells display enhanced apoptosis resistance in response to conventional chemotherapies and TRAIL. Hence, our data show that SOX2 associates with stem cell state in ovarian carcinoma and induction of SOX2 imposes CSC properties on SOC cells. We propose the existence of SOX2-expressing ovarian CSCs as a mechanism of tumor aggressiveness and therapy resistance in human SOC.

IκBζ is a regulator of the senescence-associated secretory phenotype in DNA damage- and oncogene-induced senescence.

Cellular senescence, a state of sustained cell cycle arrest, has been identified as an important anti-tumor barrier. Senescent cells secrete various growth factors and cytokines, such as IL6 and IL8, which collectively constitute the senescence-associated secretory phenotype (SASP). The SASP can signal to the tumor environment and elicit the immune-mediated clearance of tumor cells or, depending on the context, could potentially promote tumor progression. Despite the importance of the SASP to tumor biology, its regulation remains relatively unknown. Here, we show that IκBζ, an atypical member of the inhibitor of NFκB proteins and selective coactivator of particular NFκB target genes, is an important regulator of SASP expression. Several models of DNA damage- and oncogene-induced senescence revealed a robust induction of IκBζ expression. RNAi-mediated knockdown of IκBζ impaired IL6 and IL8 expression, whereas transgenic IκBζ expression resulted in enhanced SASP cytokine expression. Importantly, during senescence of IκBζ knockout cells induction of IL6 and IL8, but not of the cell cycle inhibitor p21(WAF/CIP1), was completely abolished. Thus, we propose an important and hitherto unappreciated role of IκBζ in SASP formation in both DNA damage- and oncogene-induced senescence.

IκBζ is a transcriptional key regulator of CCL2/MCP-1.

CCL2, also referred to as MCP-1, is critically involved in directing the migration of blood monocytes to sites of inflammation. Consequently, excessive CCL2 secretion has been linked to many inflammatory diseases, whereas a lack of expression severely impairs immune responsiveness. We demonstrate that IκBζ, an atypical IκB family member and transcriptional coactivator required for the selective expression of a subset of NF-κB target genes, is a key activator of the Ccl2 gene. IκBζ-deficient macrophages exhibited impaired secretion of CCL2 when challenged with diverse inflammatory stimuli, such as LPS or peptidoglycan. These findings were reflected at the level of Ccl2 gene expression, which was tightly coupled to the presence of IκBζ. Moreover, mechanistic insights acquired by chromatin immunoprecipitation demonstrate that IκBζ is directly recruited to the proximal promoter region of the Ccl2 gene and is required for transcription-enhancing histone H3 at lysine-4 trimethylation. Finally, IκBζ-deficient mice showed significantly impaired CCL2 secretion and monocyte infiltration in an experimental model of peritonitis. Together, these findings suggest a distinguished role of IκBζ in mediating the targeted recruitment of monocytes in response to local inflammatory events.

Fumarates improve psoriasis and multiple sclerosis by inducing type II dendritic cells.

Fumarates improve multiple sclerosis (MS) and psoriasis, two diseases in which both IL-12 and IL-23 promote pathogenic T helper (Th) cell differentiation. However, both diseases show opposing responses to most established therapies. First, we show in humans that fumarate treatment induces IL-4-producing Th2 cells in vivo and generates type II dendritic cells (DCs) that produce IL-10 instead of IL-12 and IL-23. In mice, fumarates also generate type II DCs that induce IL-4-producing Th2 cells in vitro and in vivo and protect mice from experimental autoimmune encephalomyelitis. Type II DCs result from fumarate-induced glutathione (GSH) depletion, followed by increased hemoxygenase-1 (HO-1) expression and impaired STAT1 phosphorylation. Induced HO-1 is cleaved, whereupon the N-terminal fragment of HO-1 translocates into the nucleus and interacts with AP-1 and NF-κB sites of the IL-23p19 promoter. This interaction prevents IL-23p19 transcription without affecting IL-12p35, whereas STAT1 inactivation prevents IL-12p35 transcription without affecting IL-23p19. As a consequence, GSH depletion by small molecules such as fumarates induces type II DCs in mice and in humans that ameliorate inflammatory autoimmune diseases. This therapeutic approach improves Th1- and Th17-mediated autoimmune diseases such as psoriasis and MS by interfering with IL-12 and IL-23 production.

PINK1/Parkin-mediated mitophagy is dependent on VDAC1 and p62/SQSTM1.

Parkinson's disease is the most common neurodegenerative movement disorder. Mutations in PINK1 and PARKIN are the most frequent causes of recessive Parkinson's disease. However, their molecular contribution to pathogenesis remains unclear. Here, we reveal important mechanistic steps of a PINK1/Parkin-directed pathway linking mitochondrial damage, ubiquitylation and autophagy in non-neuronal and neuronal cells. PINK1 kinase activity and its mitochondrial localization sequence are prerequisites to induce translocation of the E3 ligase Parkin to depolarized mitochondria. Subsequently, Parkin mediates the formation of two distinct poly-ubiquitin chains, linked through Lys 63 and Lys 27. In addition, the autophagic adaptor p62/SQSTM1 is recruited to mitochondrial clusters and is essential for the clearance of mitochondria. Strikingly, we identified VDAC1 (voltage-dependent anion channel 1) as a target for Parkin-mediated Lys 27 poly-ubiquitylation and mitophagy. Moreover, pathogenic Parkin mutations interfere with distinct steps of mitochondrial translocation, ubiquitylation and/or final clearance through mitophagy. Thus, our data provide functional links between PINK1, Parkin and the selective autophagy of mitochondria, which is implicated in the pathogenesis of Parkinson's disease.

Analysis of differential DNA damage in the mitochondrial genome employing a semi-long run real-time PCR approach.

The maintenance of the mitochondrial genomic integrity is a prerequisite for proper mitochondrial function. Due to the high concentration of reactive oxygen species (ROS) generated by the oxidative phosphorylation pathway, the mitochondrial genome is highly exposed to oxidative stress leading to mitochondrial DNA injury. Accordingly, mitochondrial DNA damage was shown to be associated with ageing as well as with numerous human diseases including neurodegenerative disorders and cancer. To date, several methods have been described to detect damaged mitochondrial DNA, but those techniques are semi-quantitative and often require high amounts of genomic input DNA. We developed a rapid and quantitative method to evaluate the relative levels of damage in mitochondrial DNA by using the real time-PCR amplification of mitochondrial DNA fragments of different lengths. We investigated mitochondrial DNA damage in SH-SY5Y human neuroblastoma cells exposed to hydrogen peroxide or stressed by over-expression of the tyrosinase gene. In the past, there has been speculation about a variable vulnerability to oxidative stress along the mitochondrial genome. Our results indicate the existence of at least one mitochondrial DNA hot spot, namely the D-Loop, being more prone to ROS-derived damage.

Parkin protects mitochondrial genome integrity and supports mitochondrial DNA repair.

Mutations in the parkin gene are the most common cause of recessive familial Parkinson disease (PD). Parkin has been initially characterized as an ubiquitin E3 ligase, but the pathological relevance of this activity remains uncertain. Recently, an impressive amount of evidence has accumulated that parkin is involved in the maintenance of mitochondrial function and biogenesis. We used a human neuroblastoma cell line as a model to study the influence of endogenous parkin on mitochondrial genomic integrity. Using an unbiased chromatin immunoprecipitation approach, we found that parkin is associated physically with mitochondrial DNA (mtDNA) in proliferating as well as in differentiated SH-SY5Y cells. In vivo, the association of parkin with mtDNA could be confirmed in brain tissue of mouse and human origin. Replication and transcription of mtDNA were enhanced in SH-SY5Y cells over-expressing the parkin gene. The ability of parkin to support mtDNA-metabolism was impaired by pathogenic parkin point mutations. Most importantly, we show that parkin protects mtDNA from oxidative damage and stimulates mtDNA repair. Moreover, higher susceptibility of mtDNA to reactive oxygen species and reduced mtDNA repair capacity was observed in parkin-deleted fibroblasts of a PD patient. Our data indicate a novel role for parkin in directly supporting mitochondrial function and protecting mitochondrial genomic integrity from oxidative stress.